MONOGRAPH OF JAPANESE OPHIUKOIDEA. 29:> 



tentacle scales. I propose to distinguish the first atypical group 

 as OpliiozoncUa and the second as Haplophiura from the genuine 

 Ophiozona, the distinctive characters of the three groups being as 



follows. 



A — Disk low and flat, not nmch higher than the arm bases ; radial 

 shields separated from one another ; interbracliial ventral surfaces 

 free of granules ; genital slits long ; first ventral arm j)late smaller 

 than the following ; second oral tentacle pore opening within the 

 oral sHt ; tentacle scales present. 

 a — Disk covered with very numerous small plates, of which the larger 

 ones are surrounded by a zone of smaller ones ; a trio of disk plates 

 distinct between the outer parts of each pair of radial shields; 

 arms very gradually tapering outwards, with rather blunt extremity ; 

 dorsal, as well as ventral, arm plates almost quadrangular, widely 

 in contact with one another through almost the entire length of 



the arm OpJdozona, restr. 



aa — Disk covered with less numerous large plates mingled with smaller 

 ones ; no trio of disk plates between each pair of radial shields ; 

 arms rather rapidly tapering outwards, with very acute extremity ; 

 dorsal, as well as ventral, arm plates less well developed, separated 

 from one another by the lateral arm plates except at the arm 



base, where they may be in contact Ophlozonella. 



AA — Disk elevated high above the arm bases ; radial shields joined in 



. pairs ; interbrachial ventral surfaces closely covered with granules ; 



genital slits indistinct ; first ventral arm plate larger than the 



following ; second oral tentacle pore opening entirely outside the 



oral slit ; tentacle scales absent. HaplopJmira. 



There are two species referred to Ophiozona, viz. 0. inermis 

 Bell, 1902, and 0. capensis, Bell, 1905, which are left out of 

 account in the above key. The latter is in my opinion referable 

 to Ophiura s. str., while the former is referred to Homalophiura 

 by Clakk. 



